Add a Scheduling Protocol

- Clearly delineate the required interface of schedulers
- Useful for typing

src/xdist/dsession.py

@@ -15,6 +15,7 @@ from xdist.scheduler import LoadFileScheduling
 from xdist.scheduler import LoadGroupScheduling
 from xdist.scheduler import LoadScheduling
 from xdist.scheduler import LoadScopeScheduling
+from xdist.scheduler import Scheduling
 from xdist.scheduler import WorkStealingScheduling
 from xdist.workermanage import NodeManager
 
@@ -97,17 +98,21 @@ class DSession:
         return True
 
     @pytest.hookimpl(trylast=True)
-    def pytest_xdist_make_scheduler(self, config, log):
+    def pytest_xdist_make_scheduler(self, config, log) -> Scheduling | None:
         dist = config.getvalue("dist")
-        schedulers = {
+        if dist == "each":
-            "each": EachScheduling,
+            return EachScheduling(config, log)
-            "load": LoadScheduling,
+        if dist == "load":
-            "loadscope": LoadScopeScheduling,
+            return LoadScheduling(config, log)
-            "loadfile": LoadFileScheduling,
+        if dist == "loadscope":
-            "loadgroup": LoadGroupScheduling,
+            return LoadScopeScheduling(config, log)
-            "worksteal": WorkStealingScheduling,
+        if dist == "loadfile":
-        }
+            return LoadFileScheduling(config, log)
-        return schedulers[dist](config, log)
+        if dist == "loadgroup":
+            return LoadGroupScheduling(config, log)
+        if dist == "worksteal":
+            return WorkStealingScheduling(config, log)
+        return None
 
     @pytest.hookimpl
     def pytest_runtestloop(self):

src/xdist/scheduler/__init__.py

@@ -3,4 +3,5 @@ from xdist.scheduler.load import LoadScheduling as LoadScheduling
 from xdist.scheduler.loadfile import LoadFileScheduling as LoadFileScheduling
 from xdist.scheduler.loadgroup import LoadGroupScheduling as LoadGroupScheduling
 from xdist.scheduler.loadscope import LoadScopeScheduling as LoadScopeScheduling
+from xdist.scheduler.protocol import Scheduling as Scheduling
 from xdist.scheduler.worksteal import WorkStealingScheduling as WorkStealingScheduling

src/xdist/scheduler/each.py

@@ -103,6 +103,9 @@ class EachScheduling:
     def mark_test_pending(self, item):
         raise NotImplementedError()
 
+    def remove_pending_tests_from_node(self, node, indices):
+        raise NotImplementedError()
+
     def remove_node(self, node):
         # KeyError if we didn't get an add_node() yet
         pending = self.node2pending.pop(node)

src/xdist/scheduler/load.py

@@ -160,6 +160,9 @@ class LoadScheduling:
         for node in self.node2pending:
             self.check_schedule(node)
 
+    def remove_pending_tests_from_node(self, node, indices):
+        raise NotImplementedError()
+
     def check_schedule(self, node, duration=0):
         """Maybe schedule new items on the node.
 

src/xdist/scheduler/loadscope.py

@@ -244,6 +244,9 @@ class LoadScopeScheduling:
     def mark_test_pending(self, item):
         raise NotImplementedError()
 
+    def remove_pending_tests_from_node(self, node, indices):
+        raise NotImplementedError()
+
     def _assign_work_unit(self, node):
         """Assign a work unit to a node."""
         assert self.workqueue

src/xdist/scheduler/protocol.py

@@ -0,0 +1,47 @@
+from __future__ import annotations
+
+from typing import Protocol
+from typing import Sequence
+
+from xdist.workermanage import WorkerController
+
+
+class Scheduling(Protocol):
+    @property
+    def nodes(self) -> list[WorkerController]: ...
+
+    @property
+    def collection_is_completed(self) -> bool: ...
+
+    @property
+    def tests_finished(self) -> bool: ...
+
+    @property
+    def has_pending(self) -> bool: ...
+
+    def add_node(self, node: WorkerController) -> None: ...
+
+    def add_node_collection(
+        self,
+        node: WorkerController,
+        collection: Sequence[str],
+    ) -> None: ...
+
+    def mark_test_complete(
+        self,
+        node: WorkerController,
+        item_index: int,
+        duration: float = 0,
+    ) -> None: ...
+
+    def mark_test_pending(self, item: str) -> None: ...
+
+    def remove_pending_tests_from_node(
+        self,
+        node: WorkerController,
+        indices: Sequence[int],
+    ) -> None: ...
+
+    def remove_node(self, node: WorkerController) -> str | None: ...
+
+    def schedule(self) -> None: ...